1. Field of the Invention
The present invention relates to a multi-cylinder engine including a cam shaft linked with intake valves and exhaust valves which are disposed in a cylinder head in such a manner that one of the intake valves and one of the exhaust valves correspond to each of a plurality of combustion chambers. A crank shaft is rotatably supported by a crank case and a plurality of bearing caps are fastened to the crank case; and a transmission mechanism and configured such that an endless chain is wound around a drive sprocket fixed on the crank shaft and a driven sprocket fixed on the cam shaft.
2. Description of Background Art
A chain-type transmission mechanism for reducing a rotational power of a crank shaft to half and transmitting the reduced rotational power to a cam shaft has been known, for example, from Japanese Patent Publication No. Hei 2-60886. For a transmission mechanism using a timing belt, it is required to provide a seal structure on a crank case for preventing leakage of oil onto the transmission mechanism side. However, for the chain-type transmission mechanism, it is possible to eliminate the necessary for the provision of a seal structure on the crank case, and hence it is difficult to make the engine compact.
In the case where the transmission mechanism using an endless chain is provided between a crank shaft and a cam shaft in order to make the engine compact, it is required to turnably support one end of a chain tensioner in the longitudinal direction for the purpose of accurately transmitting power between the crank shaft and the cam shaft by bringing the chain tensioner extending in the running direction of a chain into slide-contact with the chain. However, in a multi-cylinder engine in which the crank shaft is rotatably supported by a crank case and a plurality of bearing caps, if the rotatably supporting-position of the chain tensioner is set on the crank case side, the length of the chain tensioner, that is, the length of the sliding motion of the chain tensioner on the chain is shortened so that the confinement of the action of the chain becomes difficult, and also the above rotatably supporting position is restricted.